Search This Blog

Subscribe to this blog

Follow by Email

Will Carbon Sequestration Redeem the Lawn?

Landscaping-wise, few things offend my aesthetic and ecological sensibilities quite so much as a grandiose sward of tightly mown, heavily chemically-treated grass punctuated by one or two trees and a couple of bushes. (Leaving aside, of course, the “mulch garden” topped off with a few lonely perennials.) Recently, though, I’ve learned to see some good in the approximately 40 million acres of lawn that engulf the residential landscape in the US. Caveats remain, serious ones, which I’ll get to in a bit; but the truth is, your lawn, my lawn, that of the business down the street or the corporate campus in a nearby suburb, serves as a carbon sink of modestly robust proportions.

This is important, because these days any plan for keeping the average global temperature from going up more than 3.6 degrees (2 degrees C) now involves active carbon sequestration. We’ve dilly-dallied so long that while heading off extreme global warming and all the misery it will entail could once have involved fairly modest efforts, now much more is required, and faster. So much CO2 and other greenhouse gases permeate the atmosphere that cutting emissions to zero will no longer suffice. We must go carbon negative; but there still exists no feasible technological way to do this at any kind of scale. Yet carbon sequestration is what natural ecosystems do all the time; in general, the healthier the ecosystem, and the more full of life its soil, the more carbon it sequesters.Hence, if we expect to be successful, it will be by working with natural systems, through reforestation, grassland restoration, natural area conservation and expansion, and changing agriculture practices to enhance soil health and thus carbon sequestration.

Here is where lawns come in, and where anyone with a lawn can help, within certain parameters. In the US, lawns, including golf courses and playing fields, are considered part of croplands, 5% of the total, to be exact. On average, lawns sequester about 0.5 to 1.5 Mg carbon, per hectare per year (a hectare equals 2.2 acres) as opposed to an average cropland rate of 0.3 MG C per hectare per year. A standard comparison by defenders of turfgrass is that soil carbon sequestration rates compare favorably with natural grasslands, especially if the lawn is looked after through mowing, watering, and adding inputs of various kinds. Inputs vary widely and could be anything from simply leaving clippings on the lawn after mowing and other organic measures to the full panoply of fossil fuel derived fertilizers and pesticides on offer, and what they are is rarely specified in the literature.

According to one study, even after subtracting the hidden carbon costs involved in using power lawn mowers, other power tools and fossil-fuel-based chemical inputs, lawns still sequester carbon. Another study comparing the carbon sequestration capabilities of lawns in Colorado with natural shortgrass prairies found that lawns actually beat the prairies in their carbon storage amounts. But as the authors point out, this is with careful tending and involves using quite a bit of water. Lawns would not survive in that arid region without human intervention, whereas the prairie has been self-sufficient and sequestering carbon for thousands of years. Furthermore, turfgrass has an average root-depth of only four inches or so, leading me to wonder about lawns’ capabilities for deep carbon storage of the kind at which deep-rooted prairies excel, with their diverse and prolific soil communities. And in healthy woodlands, though much of the carbon is locked up in the trees, vast underground networks of fungi and other denizens of the living soil enable carbon to translocate deep in the ground.

When I first heard of lawns’ carbon sequestration potential, it seemed hard to believe, since a classic high-input lawn is a sort of biological null, at least as far as general biodiversity is concerned, but this actually makes sense. Grass is a perennial, one that “armors” the soil. The natural death and regeneration of its roots add biomass, as does leaving the clippings on after mowing, which enables the soil biome to thrive and carbon to be stored, at least within the top fifteen inches. Planted in a geographically favorable location, a lawn can be maintained with little effort and, once planted and established, there’s little to no soil disturbance. So a lawn, once planted and reasonably cared for will immediately start sequestering carbon, and keep doing so for at least twenty-five to thirty years, until a saturation point is reached.

Unlike some folks I know, I’ve never been absolutely against an appropriately sized and placed lawn, though intensely against the use of synthetic fertilizer and pesticides. Surrounded as it is by large beds of native plants, my own backyard lawn is a small part of the garden, not the extent of the landscaping—a crucial difference. Though it grows well and stays green without irrigation or synthetic inputs, my lawn would fail in the eyes of the pristine lawn brigade, since within its boundaries grow a medley of white clover, early spring bulbs, violets, a few dandelions and a little plantain and creeping Charlie. Thus it earns its ecological keep. Those other species of plants both increase the lawn’s carbon storage potential and help increase ecosystem interactions. The clover’s deep roots fix nitrogen and help the soil retain moisture during dry periods. When in bloom, the bulbs (snowdrops and scilla), violets, clover and even dandelions and creeping Charlie benefit pollinators. The whole expanse thrives with only organic inputs: clippings left on after mowing, overseeding with grass and clover seed every few springs, and top-dressing with home made compost spring and fall (if I get to it). The black, carbon-rich soil soil is eminently healthy, and earthworms abound. There’s no nitrogen or phosphorus run off, little to no methane or nitrous oxide emissions, and no hidden carbon costs either: we use a push lawn mower and hand rakes.

All of this is easy because the Chicago area where I live is one of the few areas of the US that qualify as a turfgrass sweet spot. It’s one of the places temperate enough, with enough natural rainfall and good enough soil conditions that grass can grow happily, all by itself, with little to no help from humans. In much of the country, however, irrigation and intensive inputs, synthetic or organic, are required to keep lawns lush, at a steep environmental cost exacerbated by mono-culture-only aesthetic requirements. These costs are so high that in many cases the soil carbon sequestration benefits lawns offer do not, overall, balance the scales in their favor. If a lawn can’t survive without a serious care regime, especially extra watering, perhaps its best not to have a lawn, per se, regardless of how much carbon it may sequester.

Credit: Melisi et al

Because of these high costs, a movement way from lawns is slowly taking place. In arid regions across the western half of the continent where lawn irrigation can easily take 50-75% of a household’s water usage, over the past few years communities have been restricting outdoor water use.Graywater systems are on the rise. Residents are encouraged to put in ecosystem-appropriate xeriscaping as a substitute for grass, which can thrive without stressing town water supplies. Fertilizers and pesticides are being looked at, too, since they continue to contribute to a variety of ecological ills such as failing soil health, release of nitrous oxide, coastal dead zones and toxic algae blooms. Golf courses, schools and park districts are starting to reassess the use of synthetic inputs and some are switching to organic methods. Yet homeowners are proving slow to follow suit, and the ideal of a green front lawn, even where it geographically doesn’t belong, is proving surprisingly resistant to revision.

It’s interesting to imagine a US where manicured turfgrass lawns ceased being a universal requirement in landscaping, supposedly applicable to all regions, everywhere (though other species of grass, such as St. Augustine, might be used in the south). What other kinds of carbon-sequestering plants could be used in the area in front of the typical suburban house? There are native groundcovers and sedges that thrive in Texas, and shortgrass prairie flowers and grasses such as buffalo grass flourish across the plains. What kinds of regionally appropriate landscaping would arise? Could thirsty Colorado lawns be replaced with native prairie species?

Even in a grass-friendly region, grass is not appropriate in every situation. My small front yard became too shady for a lawn, thanks to a pair of maples in the parkway. It now sports a small, spring blooming serviceberry tree surrounded by woodland sedges interspersed with low growing spring wildflowers. It is very much a work in progress and will take a few years to fill in. Yet I feel confident that carbon sequestration is going on in and will continue to do, no inputs required. Let golf course owners and playing field managers wrestle with the correct balance of water and inputs that would achieve carbon sequestration while keeping their fields green.At least there the grass is being used for something besides viewing purposes only. In general, in most parts of the country, a landscaped area of low maintenance, eco-system friendly plants (preferably species native to the area) remains a better choice than a lawn.

Comments

I'm a little surprised to read this about carbon sequestration by lawns. I wonder how they compare to tall grass prairie grasses and forbs that grow in our garden. I still have some lawn, full of "weeds" like yours. I would only add that there is no such thing as a "little" creeping charlie.

Hi Jason,Thanks for your comment. I agree about the surprise factor. There is a lot of work that needs to be done on this topic, especially deep carbon sequestration. Re creeping Charlie, yes it can get rampant, particularly in years with mild winters. In my own yard, I don't have much of a problem with it in the sun; damp shade is another issue entirely--one reason I decided to stop trying to grow grass in the shady front. For some reason it seems easier to control in the areas thickly planted with native plants.

Adrian: This article and "What does synthetic fertilizer have to do with it?" hit the proverbial nail on the head. After years of research and experimentation, I can tell you there is little hope for lawn carbon sequestration until we put the synthetic fertilizer away, diversify the typical lawn in terms of plants, and inoculate the soil typically with good compost to restart the incredible soil microbe and plant (root) interaction required. After hearing Dr. Christine Jones speak and studying the Morrow Plot data of University of Illinois, it is obvious we started down the wrong road 50 years ago and it is hard for us to turn back. Thanks for the great information!

Hi Larry, Thanks. Yes, and if we could only add managed grazing to suburbia! :)

It would be interesting to find out from suburban chicken owners how their birds impact their lawns. I've got a friend who does a three-year rotation in his (extensive) vegetable garden that incorporates his laying hens foraging in the fallow section. I'll have to talk to him more about this.

Adrian, i would be very interested in seeing the two studies you mention in paragraph 4. I'm trying to build a case, for or against, turf-to-prairie conversions from the standpoint of carbon sequestration. From other standpoints, the benefits are obvious. thank you - Devin Floyd (Center for Urban Habitats)

I'm working in the research phase of a documentary (think James Burke's Connections series) on issues related to many of the topics discussed on your site. I'm "weeding" through the vast reserves of content available on the web and through governmental agencies as well as for and non-profit organizations.

There is a wealth of information and a myriad of diverse opinions/studies related to current changes affecting the environment, habitat, species and natural resources. Lots of micro perspectives, lots of niche resources. What I'm not finding is much information with a macro perspective.

Have you come across an article, a website, a research paper or a book that connects the various interrelated issues into a holistic "big picture" perspective?

Popular Posts

Part two of a series exploring how regenerative gardening techniques can enhance carbon storage while improving soil health. In part one I discussed some of the principles behind the factors involved in soil health and how plants and the soil biological community work together to store carbon and build appropriate fertility. “Why Not Start Today: Backyard Carbon Sequestration Is Something Nearly Everyone Can Do” can be found here.

A brief digression about the term “regenerative gardening”
So what is regenerative gardening, anyway? Regenerative gardening is an umbrella term that embraces many styles and traditions of organic cultivation and adds explicit intentionality regarding carbon sequestration. The recent Rodale white paper, “Regenerative Organic Agriculture and Climate Change,” says that, “regenerative organic agriculture refers to working with nature to utilize photosynthesis and healthy soil microbiology to draw down greenhouse gases.” The same goes for gardening. Like regene…

Gardeners new to the concept of carbon gardening often ask these two questions: What good soil management strategies will help maximize carbon sequestration? And, what would be a good plant palette to help accomplish this? Good questions both, to which I wish I could give detailed, specific answers. Carbon gardening in northern Illinois, where I live, differs from carbon gardening in other regions; each will require region-specific strategies and plant palettes. Everything depends on where the gardener lives and the conditions in which they are gardening. Thus, what follows is more in the way of a general discussion that might help point in the right direction than a series of rigid prescriptions.

Organic carbon sequestration is one of the oldest tricks in nature’s ancient playbook for global ecosystem regulation. These days, as we search for ways to pull excess carbon out of the atmosphere in order to mitigate global warming, new attention has focused on “natural climate solutions,”…

Our bee problem is quite the topic of conversation these days--at social gatherings, in meetings, over coffee. Everyone agrees we should save the bees, though many of us think of them in the abstract as little buzzing yellow flying things, maybe as cartoon characters, or as creatures that exist to help us.

I could say, and have—for example at Christmas dinner when apologizing for my not-quite-stellar pumpkin bread—that last summer the CSA grower from whom I get my produce planted five hundred pumpkin plants and only got three pumpkins (so I had to buy canned, rather than processing my own). No pollination, he thought. And just the other day an acquaintance mentioned that friends who live in a tony suburb north of Chicago had, also last summer, had their own pollination troubles in their vegetable garden. Why? she wondered.

“Shrubbiness is such a remarkable adaptive design that one may wonder why more plants have not adopted it.” (H. C. Stutz, 1989)

In light of the newest IPCC and US climate change reports, coupled with reports of the ongoing declines of wild species—birds, insects—you name them, just so long as they aren’t human, I have turned to thinking about shrubs. It is precisely their adaptive characteristics that give shrubs their potential to be powerful players in soil carbon sequestration and ecosystem regeneration in certain parts of the world, such as the Midwest.

Although alarming, the reports are not surprising to anyone who’s been keeping track. The IPCC report says human global society has 12 years to reduce carbon emissions to 45% below 2010 levels if there is to be any hope of holding overall average global temperature rise to 1.5 degrees C (2.7 degrees F). The US report, searchable by region, adds fairly detailed, equally dire scenarios for this country. No place on earth will be immu…

During a recent conservation/climate change seminar, I happened to comment about the relationship of home gardens to natural areas; how we need to cease thinking of nature as being something over there, while our private yards and gardens are treated as separate; and how our gardens can help sequester carbon. Afterward, a woman came up to me, someone who had spoken knowledgeably about habitats, biodiversity of prairies, and the difference between C4 and C3 plant species. “Without using herbicides,” she said, “What am I to do about the creeping Charlie in my lawn? I just hate it.”

A fellow gardener and I tried to explain: a polyculture lawn is ok—herbiciding creeping Charlie not worth the environmental cost (besides which it’s nearly indestructible)—it’s easy to pull up—it mostly grows in shady areas where grass has difficulty—bees like the flowers—looks nice in spring—don’t fight it…Well, she wasn’t going to hand weed it, thought she was allergic to it and lawns shouldn’t have flower…

Part one of a series about using regenerative gardening techniques to enhance carbon storage while improving soil health.

To make it simple as a crayon sketch, there are two ways to mitigate climate change that, in tandem, could work. One is to lower emissions. To decarbonize, if you will—and de-nitrous oxide-ize, de-methane-ize, and de-soot-ize as well. It is true that to keep the earth’s average temperature from warming more than 2° C (3.6° F), emissions will have to fall. Drastically. Which means lifestyles, in fact whole cultures and economies, will have to change, and everyone, especially the well off, will have to share in the sacrifices and changes to be made. This necessity is the real inconvenient truth implied by the inconvenient truth of climate change and one mostly being ignored or rationalized away by pretty much everyone, except a small percentage of realists. Part of the problem, I think, might not be so much willful ignorance as a failure of imagination. Quite a few …

"We are the children of our landscape; it dictates behavior and even thought in the measure to which we are responsive to it." (Lawrence Durrell)

As I write, it’s the first day of spring. I’ve been busy with tasks ordained by the season: checking the gardens for winter damage, deciding what flats of sedges and flowers to order, starting seeds in the greenhouse and considering what vegetables to put in. The sap is finally rising; the tall maples have gone fuzzy at the tips of their branches, as they do when in bloom, and the bur oaks have developed the sort of knobbly look on their twigs that announces the swelling of buds. The trees are moving more limberly in response to the wind after prolonged winter stiffness. Still, everything remains, briefly, just barely, in abeyance before the sudden mad rush of April and May.

Right now, I’m supposed to be answering some basic questions posed by a person new to native plant gardening: How do you start learning about native plants? I…